Copolyester-carbonate resins are known thermoplastic materials which, due to their many advantageous properties, find use as thermoplastic engineering materials in a wide variety of applications. The copolyester-carbonates exhibit, for example, excellent properties of toughness, flexibility, high heat distortion temperatures, and optical transparency. However, these resins, due to their relatively high melt viscosities, are generally relatively difficult to process. Various additives can be added to these resins in order to improve their processability. The addition of these additives, while generally being effective in improving the processability of the resins, sometimes adversely affects some of their other advantageous properties such as, for example, their heat distortion temperatures and their optical transparency. It would thus be very advantageous if copolyester-carbonates could be provided which were easier to process and simultaneously retained their high heat distortion temperatures and their optical transparency.
It is, therefore, an object of the instant invention to provide copolyester-carbonate resin compositions which are easier to process and which yet retain their relatively high heat distortion temperatures and their optical properties such as transparency.